Either the GM is pulling our leg, and there's a hidden sub-quest somewhere within the word "map," or there's a trick related to the Uithors map.
Because, according to Wikipedia:
White Horse (cave) is a cave located in the Arabika mountain range in Abkhazia.
White Horse (whisky) is a brand of Scottish whisky.
Whitehorse is the capital and largest population center of the Canadian territory of Yukon.
The Uffington White Horse is a chalk figure 110 m long near the village of Uffington in the English county of Oxfordshire.
The "White Horse Final" is the final match of the 1923 FA Cup.
White Horse (film) is a short film by Baras Khalzanov.
White Horse (gallery) is a gallery of contemporary art in Gelendzhik.